Boiling Heat-Transfer Performance at Critical Water Level in a Porous Bed

An experimental investigation has been conducted to determine boiling heat-transfer performance at the critical water level in a porous bed. The porous bed contained in a vertical circular cylinder was made up of packed spherical beads whose diameters ranged from 2.0 to 16.2 mm. Four kinds of the particles of glass, alumina, steel, and copper beads were adopted as the testing beds. Measurements were carried out as the temperature difference ΔTs between the heating surface and saturated water varied from 0.2 to 8.3 K. It was observed that there might be a critical water level at which a maximum boiling heat-transfer coefficient took place for a given ΔTs. The critical water-level condition was carefully obtained by injecting the saturated water. The boiling heat flux was found to be relatively independent of ΔTs for smaller ΔTs values, while it tends to level off as ΔTs increases for small bead diameters.